Drivetrains for hybrid automotive vehicles may be configured and operated in several ways. As an example, U.S. Pat. No. 5,993,351 to Deguchi et al. discloses a first electrical motor mechanically connected to an engine and a second electrical motor mechanically connected to the engine through a clutch. Motive force is transmitted from the second electrical motor to drive wheels through a transmission. It is decided whether to release the clutch based on a detected vehicle speed and a detected required motive force. Engine output at that time is estimated. The second electrical motor is controlled such that generated torque corresponds to the estimated engine output if it is decided to release the clutch. The first electrical motor is controlled such that the torque generated by the second electrical motor is absorbed.
As another example, U.S. Pat. No. 6,041,877 to Yamada et al. discloses a drive unit for a hybrid vehicle. The drive unit includes an internal combustion engine, a transmission connected to the internal combustion engine via a clutch and a primary differential gear for distributing a driving force transmitted from the transmission to primary driving wheels. The drive unit also includes a transfer connected to the primary differential gear for taking out a part of the driving force transmitted from the transmission to the primary differential gear, a pair of propeller shafts for transmitting part of the driving force from the transfer to a secondary differential gear, and an electric motor provided between the propeller shafts. The drive unit further includes a pair of clutches, each connecting the electric motor to one of the pair of propeller shafts.
As yet another example, U.S. Pat. No. 6,190,282 to Deguchi et al. discloses a first electric motor connected mechanically to an engine and a second electric motor connected mechanically through a clutch to the engine. Drive force is transmitted to drive wheels through a transmission from the second electric motor. It is decided whether to connect the clutch on the basis of driving conditions. The engine is controlled so that the output of the engine meets the required force when it is decided to connect the clutch. The first electric motor functions as an electric generator such that the rotation speed of the engine reaches a target rotation speed. The clutch is connected when the engine is rotating at a target rotation speed.